1. Field of the Invention
The present invention relates to novel single-phase and amorphous polymeric blends, well adapted for the production of molded shaped articles therefrom, comprising a major amount of an amorphous semiaromatic polyamide prepared from at least one alkylpentamethylenediamine and aromatic dicarboxylic acid(s) and a minor amount of a semicrystalline polyamide of nylon type prepared from hexamethylenediamine, adipic acid and/or .epsilon.-caprolactam. The present invention also relates to a process for the preparation of such novel polymer blends.
2. Description of the Prior Art
Wholly aliphatic linear polyamides of nylon type, of high molecular weight, have many physical and chemical properties which make them suitable for production of a wide variety of shaped articles such as fibers, films and other molded objects.
Polyhexamethylene adipamide, or nylon 66, is one example of a polyamide which has been developed very extensively. However, these polymers exhibit a number of defects, the significance of which is a function of the intended use thereof. In the majority of cases, these polyamides are semicrystalline polymers and are therefore not transparent, and they cannot be employed in fields of application which require transparency. Furthermore, these polyamides generally exhibit a shrinkage on molding, which may be significant, a water uptake which can be considerable and, as a corollary, a dimensional stability to moisture which may be insufficient and mechanical properties which are adversely affected by the surrounding moisture and which also deteriorate at temperatures above 100.degree. C., because of the low value of their glass transition temperature Tg (which is generally below 80.degree. C.).
A great many patents describe polyamides which have different recurring units such as, particularly, polyamides comprising mixed aliphatic and aromatic recurring units, which make it possible to wholly or partially avoid those shortcomings described above. The introduction of aromatic rings provides an increase in the melting or softening point and in the Tg, resulting particularly in a better retention of mechanical properties at high temperatures. Moreover, when their composition is altered, these polyamides may be amorphous polymers.
Typical amorphous semiaromatic polyamides include, for example, the copolymers prepared from hexamethylenediamine and isophthalic (60 to 90 mol % in the mixture of the diacids) and terephthalic acids (cf. U.S. Pat. No. 3,382,216), which exhibit a Tg on the order of 100.degree. C. to 120.degree. C., and the copolymers prepared from 2-methylpentamethylenediamine and isophthalic (15 to 30 mol % in the mixture of the diacids) and terephthalic acids (cf. FR-A-2,325,673), which exhibit a Tg on the order of 137.degree. C. to 142.degree. C. However, because of high melt viscosities, the conversion of these amorphous semiaromatic polyamides by a melt route, for example by injection molding, requires a high processing temperature which is liable to retard their development. This temperature is, for example, on the order of 280.degree. C. to 300.degree. C. in the case of the above-mentioned copolymers prepared from hexamethylenediamine and aromatic acids, and from 290.degree. C. to 310.degree. C. in the case of the above-mentioned copolymers prepared from 2-methylpentamethylenediamine and aromatic acids.
Furthermore, semiaromatic polyamides exhibit a very low shrinkage which frequently leads to difficulties in the operations of demolding the shaped articles produced therefrom.
Thus, serious need continues to exist in the semiaromatic polyamide art for improved polyamide compositions exhibiting at least the following combination of the properties:
(i) adapted for use in fields of application which require an excellent transparency; PA1 (ii) having a Tg higher than 100.degree. C. such as to permit the production, for example by injection molding, of shaped articles exhibiting better polymer stability and better retention of mechanical properties at elevated temperatures, relative to compositions prepared from a polyamide of nylon type; PA1 (iii) being easily converted by a melt route at a processing temperature which is not too high, of the type utilizing temperatures ranging from 270.degree. C. to 290.degree. C., because of a melt viscosity which is less than that of a semiaromatic polyamide; and PA1 (iv) offering, where appropriate, a slight molding shrinkage, the degree of which is greater than that obtained in the case of the semiaromatic polyamide, but less than that obtained in the case of a polyamide of nylon type, such as to facilitate demolding of the shaped articles produced therefrom. PA1 (a) in addition to satisfying the aforesaid objective, especially as regards the requirements concerning transparency, Tg values and conversion conditions discussed above; PA1 (b) the realization of resilience properties which, on the one hand, are superior to those provided by the semiaromatic polyamide used alone in the case of analysis temperatures ranging from room temperature 23.degree. C.) to temperatures as low as those ranging, for example, from 0.degree. C. to -25.degree. C. and, on the other hand, remain substantially constant throughout this temperature interval ranging from room temperature to, for example, -25.degree. C. PA1 (i) an amorphous semiaromatic polyamide, which may be a homo- or a copolymer, which comprises the recurring structural units of the formulae (I), (II), (III) and (IV): ##STR1## and wherein the structural units of formulae (II) and (IV) are optional; the molar ratio of the units (I)+optionally (II) relative to the sum of the units (III)+optionally (IV) is equal to 1; the amount of the units (II) in the mixture of (I)+(II) ranges from 0% to 15 mol %, and that of the units (I), relative to the same mixture, ranges from 100% to 85 mol %; and the amount of the units (IV) in the mixture of (III)+(IV) ranges from 0% to 90 mol %, and that of the units (III), relative to the same mixture, ranges from 100 to 10 mol %; and PA1 (ii) a semicrystalline polyamide of nylon type, which may be a homo- or copolymer, which comprises nylon 66 (polymer of hexamethylenediamine and of adipic acid), nylon 6 (polymer of .epsilon.-caprolactam), mixtures of such polymers and copolymers obtained from the monomers used for the preparation of nylons 66 and 6; with the proviso that (iii) the amount of the semicrystalline polyamide (ii) constitutes not more than 40% of the weight of the combination of semiaromatic polyamide (i)+semicrystalline polyamide (ii).